TREES OF AMERICA. 27 



and nearly the size of an egg, that are often 

 found sticking to the branches ; they are 

 caused by a fly which pierces the bark and 

 leaves its eggs in the hole ; in a little while 

 the bark swells, and forms the oak-apple, or 

 gall, as some people call it ; the diers make 

 great use of these galls ; I dare say you have 

 picked them up very often ; they are full of a 

 sort of dusty pith. And now, boys, I believe 

 I have told you the principal uses of the oak ; 

 if you like I will describe some of the different 

 kinds to you." 



" Are there many different sorts of oak, 

 Uncle Philip ?" 



" Yes, a great many ; but they differ from 

 each other mostly in the shape of the leaves. 

 In North America, forty-four kinds have been 

 described, some of which bear fruit every 

 year, and some only once in two years. The 

 principal kinds are the white oak, the black, 

 the red. and the live oak ; the others are 

 mostly varieties of these four. 



" The white oak is found chiefly in the 

 Middle States, and is most abundant in Penn- 

 sylvania ; it grows seventy or eighty feet 

 high, and the trunk is from three to seven 

 feet thick j the bark is white, with large black 



